The present invention relates to electroluminescent (EL) lamps and more particularly to an EL lamp in the form of an adhesive label that can be mechanically applied and electrically connected to a surface or substrate through the use of conductive and non-conductive pressure sensitive adhesive (PSA). Adhesive labels used herein is to be broadly construed to include stickers and pressure sensitive films.
EL lamps are basically devices that convert electrical energy into light. AC current is passed between two electrodes insulated from each other and having a phosphorous material placed therebetween. Electrons in the phosphorous material are excited to a higher energy level by an electric field created between the two electrodes during the first quarter cycle of the AC voltage. During the second quarter cycle of the AC voltage, the applied field again approaches zero. This causes the electrons to return to their normal unexcited state. Excess energy is released in the form of light when these electrons return to their normal unexcited state. This process is repeated for the negative half of the AC cycle. Thus, light is emitted twice for each full cycle (Hz). Various properties of the emitted light can be controlled by varying this frequency, as well as the applied AC voltage. In general, the brightness of EL lamps increases with increased voltage and frequency.
Prior art EL lamps typically comprise numerous component layers. At the light-emitting side of an EL lamp (typically the top) is a front electrode, which is typically made of a transparent, conductive indium tin oxide (ITO) layer and a silver bus bar to deliver maximum current to the ITO. Below the ITO/bus bar layers is a layer of phosphor, followed by a dielectric insulating layer and a rear electrode layer. In some prior art EL lamps, the ITO layer is sputtered on a polyester film, which acts as a flexible substrate. A relatively thick polyester film, typically four or more mils thick is preferred because the rigidity is required for screen printing of the layers. The EL lamp construction may also include a top film laminate or coating to protect the component layers of the EL lamp construction.
The component structural layers of an EL lamp are typically made from a variety of materials. Layers are normally printed by means of a flat bed screen method and are then batch dried, except for the base substrate and top film laminate. Some of the required layers must be printed more than once in order to assure proper thickness. For example, the dielectric material needs sufficient thickness to prevent pinholes or voids, which may cause shorting between the electrodes. On the other hand, the dielectric layer is prone to cracking when multiple layers are printed one over the other. Thus, control over the printing process for the dielectric layer is extremely important. If the dielectric is too thick, the required operating voltage to achieve a given brightness will be increased as well as the chances of cracking are increased. Thus, consistent dielectric thickness in production of EL lamps is important to ensure consistent lamp brightness across a given production run of lamps.
Another limitation of a multilayer printed dielectric is the effect it has on the quality of the other component layers that are printed thereon. For example, the printed phosphor layer must be smooth and consistent to ensure a uniform lighting effect from the excited phosphor. If the multilayer printed dielectric layer is inconsistent, then the phosphor layer printed on the dielectric layer will also be inconsistent. An inconsistent printed dielectric layer will also affect other subsequently printed layers, including the transparent electrode layer. Thus, a smooth dielectric layer is important to ensure the quality of all the subsequent printed layers and ultimately the quality of the EL lamp.
Another drawback of utilizing multi-printed layers is the effect on production cycle time. Each of the printed layers of the EL lamp structure, with the exception of the base substrate and top film laminate, has to be printed and then dried before another printed layer is applied. This is a very time-consuming and expensive process, especially for printing the multilayer dielectric.
EL lamps in general, and flexible EL lamps in particular, must be easily and reliably installed in the end product or application. The EL lamp must be installed mechanically and electrically to the application. Prior art EL lamps typically treat the mechanical installation and the electrical installation separately. This typically increases manufacturing cycle times. The probability of the occurrence of manufacturing defects also increases by utilizing separate electrical and mechanical connections in the EL lamp design.
It is therefore an object of the present invention to provide an EL lamp structure in the form of an adhesive label that can be applied to a surface or object through the use of conductive and non-conductive pressure sensitive adhesive (PSA), thereby combining the electrical and mechanical installation of the EL lamp in the same manufacturing step.
It is also an object of the present invention to provide an EL lamp structure that reduces the number of printed layers by using a dielectric film in lieu of a printed dielectric layer, thus reducing the printing and drying time in the production process and increasing the reliability and quality of the EL lamp. This also eliminates the need to print on top of a thick printed dielectric layer and thereby improves the print quality of the phosphor and transparent electrode layers.
It is also an object of the present invention to provide an EL lamp structure in the form of an adhesive label that can be easily manufactured in large quantities on a continuous release liner provided in a roll or reel form.
It is also an object of this invention to provide an EL lamp structure in the form of an adhesive label that provides light from the top side as well as from the bottom side.
These and other objects and advantages of the invention will be apparent from the following description, the accompanying drawings and the appended claims.
The present invention is an EL lamp in the form of an adhesive label that can be mechanically applied and electrically connected to a surface or substrate through the use of conductive and non-conductive PSA. The EL lamp label can be easily manufactured in large quantities on a continuous release liner provided in a roll or reel form. The EL lamp label can be manufactured in large volumes and at high speeds using commercial printing, drying, laminating, punching and blanking equipment.
The EL lamp label utilizes printed structural component layers on a flexible dielectric film substrate. A phosphor layer is printed on the top of a flexible dielectric film substrate. A top transparent electrode layer, such as printable indium tin oxide (ITO), is printed on the phosphor layer. A bus bar having an electrode contact is then printed on the top transparent electrode layer. The bus bar is typically printed with silver or carbon ink or mixtures of both. A bottom electrode layer having an electrode contact is printed on the bottom of the dielectric film substrate.
A conductive pressure sensitive adhesive is applied to the electrode contact portion of the bus bar on the top of the EL lamp label and provides the necessary electrical connection for the bus bar and top electrode. A release liner can be then applied over the pressure sensitive adhesive on the electrode contact to protect the adhesive until the EL lamp label is installed. A non-conductive pressure sensitive adhesive is applied to the rear electrode layer except for the electrode contact portion. A conductive pressure sensitive adhesive is disposed on the electrode contact of the rear electrode layer and provides the necessary electrical connection for the rear electrode layer. A release liner can be then applied to the pressure sensitive adhesive on the bottom surface of the EL lamp label.